See Figure 1 for bottom case of acoustic wave imager. Maximum dimensions of bottom case are 100.00 mm * 72.00 mm x* 25.85 mm, average thickness of plastic part is 1.70 mm, material of plastic part is ABS, shrinkage rate is 1.005, and weight of plastic part is 28.26 grams. Maximum external dimension of shell product is 72.00 mm * 44.60 mm * 51.25 mm, average thickness of plastic part is 2.20 mm, and weight of plastic part is 16.32 grams. Technical requirements for plastic parts are that there shall be no defects such as peaks, underfilling, flow lines, pores, warpage deformation, silver lines, cold materials, and spray lines.

 

Figure 1 Product diagram of surface bottom shell of acoustic wave imager
Surface shell and bottom shell are key structural components of acoustic wave imager, are equipped with control components and circuit boards. Glue position at both ends of shell is a vertical plane, and demolding slope cannot be designed on the outside of shell. In this case, a large slider core must be designed to solve demoulding problem of zero-degree plane. There are buckles on four sides of shell, and it is necessary to design a lifter for demoulding. Bottom shell is a closed rectangular shell. There are multiple bone positions on the top of outer side of shell and there are multiple buckle positions, it is necessary to design a sloped top for demoulding. There are many bone positions on inner edge of shell, which has a large tightening force on mold core.
Before mold design, product must first be analyzed to determine a reasonable mold opening direction. For bottom shell, difficulty of mold design is to determine opening direction of plastic part. Mold opening direction analysis is closely related to ejection of plastic parts, gate design and parting surface design. Mold opening direction selection plan determines the entire mold structure, which is related to mold manufacturing cost, mold life, injection molding cycle, size of injection molding machine, and whether automatic injection molding can be used, which will affect injection molding cost in general. Parting surface of this set of molds is not complicated. Difficulty lies in selection of mold opening direction, that is, which side of plastic part is placed on movable mold and which side is placed on fixed mold. Correct judgment will leave side with high sticking force in movable mold to facilitate ejection and demoulding of plastic parts, and design gating system on the other side. In most cases, mold opening direction can be determined by using factors such as wrapping force, and plastic parts can be left in movable mold. Inner side of bottom shell has a strong wrapping force and should be left in rear mold. However, there are many places on outer top surface of bottom shell that need to be designed with lifters. If multiple lifters are designed in the front mold, mold structure will be very complicated, ejector pins of rear mold will also be prone to whitening. Therefore, bottom shell adopts design of lifter on rear mold, and rectangular shell with a large wrapping force is left in the front mold, and front mold is drawn first to solve problem of wrapping force. See mold design shown in Figure 2.
According to customer requirements, mold design cavity layout is 1 cavity, and simplified fine nozzle mold base GCI2735 A80 B120 C120 is adopted. Panel and A plate can be separated, which is convenient for designing front mold core to shrink in advance and reduce wrapping force of plastic parts on front mold.

 

Figure 2 3D mold design

 

Figure 3 2D mold structure diagram

 

Figure 4 Structure of front mold drawing
There are many lifters on the surface shell and bottom casing. When designing lifter, it is necessary to pay attention to running direction of lifter. For some structural elements such as buckles and short grooves, there may be two or three running directions of lifter. This kind of problem requires careful thinking. Many beginners start designing without thinking, and it is easy to ignore this kind of problem. Ideal running direction of lifter is conducive to ejection and demoulding of plastic parts, which may also be related to way of injection molding. For example, in fully automatic injection molding, it must be noted that lifter does not hinder dropping of plastic part or gripping of robot. When manipulator grabs, plastic part must have a fixed orientation, cannot fall and be skewed. Manual pick-up should consider whether it is beneficial to take plastic parts with both hands, or take them with one hand. These factors must be taken into account, which is a successful mold design.
Design of slider also needs to comprehensively consider direction of slider. Two sliders of this set of molds are respectively on operating side and non-operating side of mold, which is convenient for taking parts.
Ejection of surface shell adopts lifter ejection. Ejection of bottom case adopts lifter and ejector pin.